OK, just looking at the '98 sales brochure... the V-8s all had the 3.73, the 4.10 was available behind both of the 4.0 liters, but only with the automatic trans. Flipping to the old spreadsheet at the back, it shows that the 4.10 rear end was
-Optional on the Premium Sport package only, (934A trim package). If it is a Sport, and has the fog lamps, the door keypad, the high series center console, or leather seats, then it *could* have a 4.10.
-Now, moving over to the 4-doors, the 4.10 was only optional with the V-6 equipped Eddie Bauers. Just because it's an EB doesn't mean it definitely has the 4.10, but if it's a 4-door and it's NOT an EB, it definitely not a 4.10.
In either case, the trailer towing package is not an indication of which rear end it has. The TT package included either the 3.73 or the 4.10 rear end.
That should help narrow your search anyways... Also, I can't guarantee that those facts hold true outside the 98 model year. Maybe we can get someone else to look up the other years' brochures. (I wish Ford archived 'em!)
Interesting thing though... I was looking at my window sticker, and mine included the 4.10 rear and the 'Aluminum wheels 16x7' as 'No Charge' options... Wonder why that was? Heck, there's no mention of the 16" aluminum rims anywhere to be found. Wonder if it was a late addition for the 98s?
-Joe
edit: Oh, and I didn't have the tow package either....